Ultraviolet

Ultraviolet is a set of primitives for building terminal user interfaces in Go. It provides cell-based rendering, cross-platform input handling, and a diffing renderer inspired by ncurses—without the need for terminfo or termcap databases.

Ultraviolet powers Bubble Tea v2 and Lip Gloss v2. It replaces the ad-hoc terminal primitives from earlier versions with a cohesive, imperative API that can also be used standalone.

Install

go get github.com/charmbracelet/ultraviolet@latest

Quick Start

package main

import (
	"log"

	uv "github.com/charmbracelet/ultraviolet"
	"github.com/charmbracelet/ultraviolet/screen"
)

func main() {
	t := uv.DefaultTerminal()
	scr := t.Screen()

	scr.EnterAltScreen()

	if err := t.Start(); err != nil {
		log.Fatalf("failed to start terminal: %v", err)
	}
	defer t.Stop()

	ctx := screen.NewContext(scr)
	text := "Hello, World!"
	textWidth := scr.StringWidth(text)

	display := func() {
		screen.Clear(scr)
		bounds := scr.Bounds()
		x := (bounds.Dx() - textWidth) / 2
		y := bounds.Dy() / 2
		ctx.DrawString(text, x, y)
		scr.Render()
		scr.Flush()
	}

	for ev := range t.Events() {
		switch ev := ev.(type) {
		case uv.WindowSizeEvent:
			scr.Resize(ev.Width, ev.Height)
			display()
		case uv.KeyPressEvent:
			if ev.MatchString("q", "ctrl+c") {
				return
			}
		}
	}
}

Architecture

Ultraviolet is organized as a set of layered primitives:

• Terminal — manages the application lifecycle: raw mode, input event loop, start/stop. Create one with DefaultTerminal() or NewTerminal(console, opts).

• TerminalScreen — the screen state manager. Handles rendering, alternate screen buffer, cursor, mouse modes, keyboard enhancements, bracketed paste, window title, and more. Access it via terminal.Screen().

• Screen — a minimal interface (Bounds, CellAt, SetCell, WidthMethod) implemented by TerminalScreen, Buffer, Window, and ScreenBuffer. Write code against Screen to stay decoupled from the terminal.

• Buffer / Window — off-screen cell buffers. Buffer is a flat grid of cells. Window adds parent/child relationships and shared-buffer views. Both implement Screen and Drawable.

• screen package — drawing helpers that operate on any Screen: a Context for styled text rendering (Print, DrawString, etc.) and utility functions like Clear, Fill, Clone.

• layout package — a constraint-based layout solver built on the Cassowary algorithm. Partition screen space with Len, Min, Max, Percent, Ratio, and Fill constraints.

Features

• Cell-based diffing renderer — only redraws what changed. Optimizes cursor movement, uses ECH/REP/ICH/DCH when available, and supports scroll optimizations. Minimal bandwidth, critical for SSH.

• Universal input — unified keyboard and mouse event handling across platforms. Supports legacy encodings, Kitty keyboard protocol, SGR mouse, and Windows Console input.

• Inline and fullscreen — works in both alternate screen (fullscreen) and inline mode. Inline TUIs preserve terminal context and scrollback.

• Cross-platform — first-class support for Unix (termios + ANSI) and Windows (Console API). Consistent behavior across terminal emulators.

• Suspend/resume — Stop() and Start() can be called repeatedly for suspend/resume cycles, shelling out to editors, or process suspension via uv.Suspend().

Examples

See the examples/ directory for core examples and examples/advanced/ for more complex demos.

Tutorial

See TUTORIAL.md for a step-by-step guide to building your first Ultraviolet application.

[!NOTE] Ultraviolet is in active development. The API may change.

Feedback

We'd love to hear your thoughts on this project. Feel free to drop us a note!

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• Discord
• Slack
• The Fediverse

License

MIT

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Part of Charm.

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